Anthony Arguez and Russell Vose

HINGE FIT

The Hinge Fit method, described in Livezey et al. (2007), uses a linear best fit line to define normal. The hinge point is set to 1975. Prior to 1975, the Hinge Fit is constrained to be a constant value, and after 1975, the Hinge Fit is a straight line with constant slope. Livezey et al. (2007) argue that the Hinge Fit is representative of the underlying base climate, given well-documented global changes (i.e., warming).

As with OCN, the 1940-2007 period was used for computing the 2007 Hinge Fit values. The 2007 Hinge Fit for January minimum temperature is warmer (by up to +6°C) than the 1971-2000 average for virtually every grid point in the United States (Fig. 3, top). Peak anomalies are found in the northern parts of the Midwest and Great Plains. For July maximum temperature, the Hinge Fit is generally warmer than 1971-2000 in the West, with smaller anomalies found elsewhere (Fig. 3, bottom).

Figure 3. The 2007 Hinge Fit values versus the 1971-2000 averages for January minimum temperature (top) and July maximum temperature (bottom).

6. 
   DISCUSSION
   

The results presented here all suggest that the current NOAA 1971-2000 Climate Normals are unlikely to be adequate indicators of either the current state of the climate or future climate conditions. The suite of experimental products known as Optimal Normals is an attempt to rectify this problem, and an explicit acknowledgment of the limitations of the traditional 30-year average Climate Normals.

The first wave of Optimal Normals will be available in 2009 for monthly maximum, minimum, and mean temperature for the COOP Network. NCDC plans to update these experimental Climate Normals once per year as new data values become available. In additional, a second wave of Optimal Normals are currently in the development phase, and should be available prior to the 2011 release of NOAA’s official 30-year Climate Normals for the 1981-2010 period. This will include advanced statistical techniques, as well as the use of climate model projections to anticipate what Climate Normals may be in the future.

Future steps include applying significance testing to the OCN and Hinge Fit results. In addition, once all experimental products are operational, rigorous comparisons between the different Optimal Normals methods will commence. These comparative studies will guide future considerations, such as the possibility of a future official product release to complement the decadally-reported official NOAA Climate Normals.

7. 
   REFERENCES
   

Huang, J., van den Dool, H. M., and A. G. Barnston, 1996: Long-Lead Seasonal Temperature Prediction Using Optimal Climate Normals. J. Clim., 9, 809-817.

Livezey, R. E., Vinnikov, K. Y., Timofeyeva, M. M., Tinker, R., and H. M. van den Dool, 2007: Estimation and Extrapolation of Climate Normals and Climate Trends. J. Appl. Meteor. and Clim., 46, 1759-1776.

Menne, M. J., and C. N. Williams, Jr., 2008: Homogenization of Temperature Series via Pairwise Comparisons. J. Clim., in press.

Menne, M. J., Williams, Jr., C. N., and R. S. Vose, 2008: The United States Historical Climatology Network Monthly Temperature Data – Version 2. Bull. Amer. Meteor. Soc., in press.

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